Processing Unit Incorporating Special Purpose Register for Use with Instruction-Based Persistent Vector Multiplexer Control

ABSTRACT

A software-accessible special purpose register is architected into a processing unit in order to implement persistent vector multiplexer control of a vector-based execution unit. A persistent swizzle instruction is defined in an instruction set for the vector-based execution unit and is used to cause state information to be stored in the special purpose register such that the operand vectors processed by subsequent vector instructions executed by the vector-based execution unit will be selectively shuffled using the persisted state information. As a result, when multiple vector instructions require a common custom word ordering for one or more operand vectors, a single persistent swizzle instruction may be used to select the desired custom word ordering for all of the vector instructions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______,filed on even date herewith by Mejdrich et al. and entitled “PROCESSINGUNIT INCORPORATING INSTRUCTION-BASED PERSISTENT VECTOR MULTIPLEXERCONTROL” (ROC920070533US1), the entire disclosure of which isincorporated by reference herein.

FIELD OF THE INVENTION

The invention is generally related to data processing, and in particularto processor architectures and execution units incorporated therein.

BACKGROUND OF THE INVENTION

As semiconductor technology continues to inch closer to practicallimitations in terms of increases in clock speed, architects areincreasingly focusing on parallelism in processor architectures toobtain performance improvements. At the chip level, multiple processorcores are often disposed on the same chip, functioning in much the samemanner as separate processor chips, or to some extent, as completelyseparate computers. In addition, even within cores, parallelism isemployed through the use of multiple execution units that arespecialized to handle certain types of operations. Pipelining is alsoemployed in many instances so that certain operations that may takemultiple clock cycles to perform are broken up into stages, enablingother operations to be started prior to completion of earlieroperations. Multithreading is also employed to enable multipleinstruction streams to be processed in parallel, enabling more overallwork to performed in any given clock cycle.

One area where parallelism continues to be exploited is in the area ofexecution units, e.g., fixed point or floating point execution units.Many floating point execution units, for example, are deeply pipelined.However, while pipelining can improve performance, pipelining is mostefficient when the instructions processed by a pipeline are notdependent on one another, e.g., where a later instruction does not usethe result of an earlier instruction. Whenever an instruction operateson the result of another instruction, typically the later instructioncannot enter the pipeline until the earlier instruction has exited thepipeline and calculated its result. The later instruction is said to bedependent on the earlier instruction, and phenomenon of stalling thelater instruction waiting for the result of an earlier instruction issaid to introduce “bubbles,” or cycles where no productive operationsare being performed, into the pipeline.

One technique that may be used to extract higher utilization from apipelined execution unit and remove unused bubbles is to introducemultithreading. In this way, other threads are able to issueinstructions into the unused slots in the pipeline, which drives theutilization and hence the aggregate throughput up. Another populartechnique for increasing performance is to use a single instructionmultiple data (SIMD) architecture, which is also referred to as“vectorizing” the data. In this manner, operations are performed onmultiple data elements at the same time, and in response to the sameSIMD instruction. A vector execution unit typically includes multipleprocessing lanes that handle different datapoints in a vector andperform similar operations on all of the datapoints at the same time.For example, for an architecture that relies on quad(4)word vectors, avector execution unit may include four processing lanes that perform theidentical operations on the four words in each vector.

The aforementioned techniques may also be combined, resulting in amultithreaded vector execution unit architecture that enables multiplethreads to issue SIMD instructions to a vector execution unit to process“vectors” of data points at the same time. Typically, a schedulingalgorithm is utilized in connection with issue logic to ensure that eachthread is able to proceed at a reasonable rate, with the number ofbubbles in the execution unit pipeline kept at a minimum.

It has been found that with vector execution units, it is oftendesirable to provide support for programmatically shuffling, orpermuting, individual elements in a vector operand for certain types ofarithmetic operations. For example, in the area of 3D image processing,backface culling can often be accelerated through the use of vectorpermutation. Backface culling is the process of determining whichtriangles that make up a 3D object face the camera, and thus, arevisible in a scene. Determining which triangles are visible allows thecomputer graphics software to spend most of its time dealing with onlyvisible faces of objects, such that performance can be maximized. As anexample, with any 3D cube, having six faces, at most three faces will bevisible from any given camera position, so it is known that at leastthree faces will not be visible in a scene and can be ignored from thestandpoint of later graphical operations such as applying textures tothe faces.

To determine if a surface of an object is facing the camera, a dotproduct of the vector that denotes where the camera is pointing, and thesurface normal vector of the surface, is calculated. Often, 3D objectsare split up into triangles with the points of each triangle vertexstored with coordinates x, y and z in a three element vector. Thesurface normals of each triangle are not usually pre-calculated. To findthis surface normal, and thus whether the triangle faces the camera, across product operation is typically performed between two vectors thatmake up two sides of the triangle, using the following equation:

${C \times T} = {{\begin{matrix}\hat{x} & \hat{y} & \hat{z} \\x_{c} & y_{c} & z_{c} \\x_{t} & y_{t} & z_{t}\end{matrix}} = \begin{matrix}{{\hat{x}\left( {{y_{c}z_{t}} - {y_{t}z_{c}}} \right)} +} \\{{\hat{y}\left( {{x_{t}z_{c}} - {x_{c}z_{t}}} \right)} +} \\{\hat{z}\left( {{x_{c}y_{t}} - {x_{t}y_{c}}} \right)}\end{matrix}}$

Conventionally, permuting elements of a vector has been performed usinga permute instruction, which operates on a vector operand stored in aregister in a register file, shuffles the elements of the vectoroperand, and stores the shuffled vector operand back into the same or adifferent register in the register file. Thus, a cross product may becomputed by a conventional vector floating point multiply add pipelineby first performing several permute instructions to move the vectorelements into the desired positions for the multiply, then performing afirst set of multiplies, then a second set, and finally performing anadd instruction with the multiply results. In order to move the vectorelements into the proper positions for the first set of multiplies, thefollowing permute instructions may be used:

[x_(t) y_(t) z_(t) w_(t)] permute1=>[z_(t) x_(t) y_(t) w_(t)]

[x_(c) y_(c) z_(c) w_(c)] permute2=>[z_(c) x_(c) y_(c) w_(c)]

[x_(t) y_(t) z_(t) w_(t)] permute3=>[y_(t) z_(t) x_(t) w_(t)]

[x_(c) y_(c) z_(c) w_(c)] permute4=>[y_(c) z_(c) x_(c) w_(c)]

If each element of each four element vector is labeled x, y, z and w,respectively, the vector elements are initially laid out in the vectorregister file in that order. The aforementioned permute instructionsmultiplex the elements into the different positions shown above inpreparation for the multiply and add operations performed later. Ofnote, the permute1 and permute2 instructions specify the same wordordering as one another, as do the permute3 and permute4 instructions.Conventional permute instructions, however, operate on single vectoroperands, and as such, a separate permute instruction is required foreach vector operand.

As noted above, a conventional permute instruction is processed byreading a vector operand from a register in a register file, shufflingthe operand elements, and writing the result back into a register in theregister file. The shuffling is performed within the execution pipelineusing a set of multiplexers. A vector arithmetic instruction then readsthe shuffled vector operand from the register file and performs thevector arithmetic.

The conventional approach, however, has a number of drawbacks. First,since the permute instruction writes back into the register file, itoccupies valuable register file space that could be used for othertemporary storage. Second, the permute instruction write back of theshuffled vector operand into the register file causes a “read afterwrite” dependency hazard condition for the later vector arithmeticinstruction, as the later instruction is required to wait for thepermute instruction to fully flow through the pipeline until it canretrieve the shuffled vector operand from the register file, whichcauses the issue logic to stall newer dependant instructions until thepermute result is ready. This stalling causes cycles to go unused in thepipeline where stages are not filled, and particularly for deeplypipelined execution units, performance can be significantly degraded.

Another approach for shuffling elements of vector operands relies onswizzle instructions. Conventional swizzle instructions may precedevector arithmetic instructions in an instruction stream to shufflevector operand elements in an execution pipeline for subsequentprocessing by vector arithmetic instructions. Swizzle instructions havethe benefit of not requiring shuffled operands to be written back to theregister file prior to use, which reduces the number of registers beingused, and avoids the read after write dependencies in the executionpipeline. However, conventional designs require a swizzle instruction tobe issued before each arithmetic instruction that requires a custom wordordering, as each swizzle instruction only specifies the custom wordordering for the immediately subsequent arithmetic instruction in theinstruction stream. The use of such instructions, however, has beenfound to unnecessarily swell the code size of instruction streams thatuse the same word ordering for multiple arithmetic instructions, andtherefore also degrades performance. In the backface culling examplediscussed above, for example, four swizzle instructions would berequired to implement the four permutes required to perform thecalculation, irrespective of the fact that only two unique word orderswere required.

A need therefore continues to exist in the art for a manner ofoptimizing the permutation of operand vectors in a vector executionunit.

SUMMARY OF THE INVENTION

The invention addresses these and other problems associated with theprior art by utilizing a software-accessible special purpose registerarchitected into a processing unit in order to implement persistentvector multiplexer control of a vector-based execution unit. Apersistent swizzle instruction is defined in an instruction set for thevector-based execution unit and is used to cause state information to bestored in the special purpose register such that the operand vectorsprocessed by subsequent vector instructions executed by the vector-basedexecution unit will be selectively shuffled using the persisted stateinformation. As a result, when multiple vector instructions require acommon custom word ordering for one or more operand vectors, a singlepersistent swizzle instruction may be used to select the desired customword ordering for all of the vector instructions.

Therefore, consistent with one aspect of the invention, a circuitarrangement includes processing logic configured to process instructionsfrom an instruction stream, where the instructions in the instructionstream are selected from an instruction set that defines a vectorinstruction and a persistent swizzle instruction. The processing logicincludes a register file including a plurality of vector registersconfigured to store operand vectors, where each operand vector includesa plurality of words, vector execution logic configured to retrieveoperand vectors from the register file and process the retrieved operandvectors responsive to vector instructions received by the processinglogic, and at least one software-accessible swizzle special purposeregister architected into the processing logic and configured to storestate information for use in selectively shuffling words from operandvectors retrieved by the vector execution logic in connection withprocessing vector instructions received by the processing logic. Thecircuit arrangement also includes swizzle logic coupled to theprocessing logic and configured to selectively shuffle words fromoperand vectors retrieved from the register file by the vector executionlogic in connection with processing of the retrieved operand vectors bythe vector execution logic. The swizzle logic is configured to, inresponse to a first persistent swizzle instruction received by theprocessing logic, persist state information for the swizzle logic in theat least one swizzle special purpose register, and to, in response to aplurality of vector instructions received by the processing logicsubsequent to reception of the first persistent swizzle instruction bythe processing logic, selectively shuffle words from operand vectorsretrieved from the register file by the vector execution logic inconnection with processing the plurality of vector instructions usingthe state information persisted in the at least one swizzle specialpurpose register.

These and other advantages and features, which characterize theinvention, are set forth in the claims annexed hereto and forming afurther part hereof. However, for a better understanding of theinvention, and of the advantages and objectives attained through itsuse, reference should be made to the Drawings, and to the accompanyingdescriptive matter, in which there is described exemplary embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of exemplary automated computing machineryincluding an exemplary computer useful in data processing consistentwith embodiments of the present invention.

FIG. 2 is a block diagram of an exemplary NOC implemented in thecomputer of FIG. 1.

FIG. 3 is a block diagram illustrating in greater detail an exemplaryimplementation of a node from the NOC of FIG. 2.

FIG. 4 is a block diagram illustrating an exemplary implementation of anIP block from the NOC of FIG. 2.

FIG. 5 is a block diagram of a processing unit incorporatinginstruction-based persistent multiplexer control consistent with theinvention, and capable of being implemented within an IP block from theNOC of FIG. 2.

FIG. 6 is a block diagram of an exemplary persistent swizzle instructionformat capable of being processed by the processing unit of FIG. 5.

FIG. 7 is a flowchart illustrating an exemplary sequence of operationsperformed by the processing unit of FIG. 5 to implementinstruction-based persistent multiplexer control consistent with theinvention.

FIG. 8 is a flowchart illustrating an exemplary sequence of operationsperformed by the processing unit of FIG. 5 in connection with a flushoperation.

FIG. 9 is a block diagram of an alternate implementation of theprocessing unit of FIG. 5, utilizing a special purpose register filearray to implement instruction-based persistent multiplexer controlconsistent with the invention.

FIG. 10 is a block diagram of an alternate implementation of theprocessing unit of FIG. 9, where the special purpose register file arrayand a portion of the swizzle control logic is maintained in a fixedexecution unit, and remote to the vector execution unit.

FIG. 11 is a block diagram of another alternate implementation of theprocessing unit of FIG. 9, where the special purpose register file arrayis maintained in a fixed execution unit, and remote to the vectorexecution unit.

FIG. 12 is a flowchart illustrating an exemplary sequence of operationsperformed by the processing unit of FIG. 9 to implementinstruction-based persistent multiplexer control consistent with theinvention.

FIG. 13 is a flowchart illustrating an exemplary sequence of operationsperformed by the processing unit of FIG. 9 to implementinstruction-based persistent multiplexer control consistent with theinvention, with additional support for duration limited persistentswizzle instructions.

DETAILED DESCRIPTION

Embodiments consistent with the invention utilize persistent swizzleinstructions to implement multiplexer control of a vector-basedexecution unit to facilitate the shuffling of words in one or moreoperand vectors processed by the execution unit.

In contrast with conventional pipelined permute type instructions thatupdate an architected register in a register array, taking up valuableregister resource and creating read after write dependencies,embodiments consistent with the invention utilize a persistent swizzleinstruction to alter the internal multiplexer control states for avector execution unit for subsequent instructions that are issued to thepipeline. The desired operand multiplexing is performed when subsequentinstructions are executing, thus allowing multiple instructions to usethe same operand multiplexing mode without a dependent permute orswizzle or multiplexer control instruction being issued for eachsubsequent instruction.

In one embodiment consistent with the invention, the multiplexer controlstate may reside internal to the vector execution unit in one or morestorage elements that are desirably precluded from read access bysoftware, so setting the state may incorporate less circuit delay andthus less instruction dependency stalling delay. In another embodimentconsistent with the invention, however, a software-accessible specialpurpose register may be used to store the multiplexer control state. Insuch an embodiment, the software accessible nature of the specialpurpose register may allow for the multiplexer control state to be savedand restored by instructions in an interrupt handler, facilitatinghandling of flush conditions without the necessity for rollback.

A storage element consistent with the invention may be implemented as alatch or register, and may be maintained internal to a vector executionunit or may be maintained externally thereto elsewhere in a processingunit. Multiple storage elements may be used to store state information,and storage elements may be associated with particular threads in amultithreaded architecture. In addition, storage elements may beinaccessible to software executing on a processing unit, e.g., so thatread access to the storage elements is precluded. Alternatively, storageelements may be software-accessible, such that software executing on aprocessing unit is able to read and/or write directly from or to suchstorage elements.

A persistent swizzle instruction consistent with the invention may beimplemented as a dedicated instruction in an instruction set, and mayinclude multiple instruction types, e.g., to set a custom word orderingbased upon a value specified in the instruction itself, or based upon avalue stored in a register referenced in the instruction. A persistentswizzle instruction may persist the selected word ordering for anunspecified duration, e.g., until a flush occurs and/or until the wordordering is modified by another persistent swizzle instruction, while insome embodiments, a persistent swizzle instruction may specify aparticular duration, e.g., in terms of subsequent instructions, suchthat a default word order is restored after a predetermined number ofsubsequent instructions are processed by the vector execution unit. Inaddition, in some embodiments, e.g., where swizzle SPR's are used, apersistent swizzle instruction may not be a separate dedicatedinstruction, but may be implemented as a store or write instruction thatidentifies a register identifier associated with a particular swizzleSPR.

Other modifications will become apparent to one of ordinary skill in theart having the benefit of the instant disclosure.

Hardware and Software Environment

Now turning to the drawings, wherein like numbers denote like partsthroughout the several views, FIG. 1 illustrates exemplary automatedcomputing machinery including an exemplary computer 10 useful in dataprocessing consistent with embodiments of the present invention.Computer 10 of FIG. 1 includes at least one computer processor 12 or‘CPU’ as well as random access memory 14 (‘RAM’), which is connectedthrough a high speed memory bus 16 and bus adapter 18 to processor 12and to other components of the computer 10.

Stored in RAM 14 is an application program 20, a module of user-levelcomputer program instructions for carrying out particular dataprocessing tasks such as, for example, word processing, spreadsheets,database operations, video gaming, stock market simulations, atomicquantum process simulations, or other user-level applications. Alsostored in RAM 14 is an operating system 22. Operating systems useful inconnection with embodiments of the invention include UNIX™, Linux™,Microsoft Windows XP™, AIX™, IBM's i5/OS™, and others as will occur tothose of skill in the art. Operating system 22 and application 20 in theexample of FIG. 1 are shown in RAM 14, but many components of suchsoftware typically are stored in non-volatile memory also, e.g., on adisk drive 24.

As will become more apparent below, embodiments consistent with theinvention may be implemented within Network On Chip (NOC) integratedcircuit devices, or chips, and as such, computer 10 is illustratedincluding two exemplary NOCs: a video adapter 26 and a coprocessor 28.NOC video adapter 26, which may alternatively be referred to as agraphics adapter, is an example of an I/O adapter specially designed forgraphic output to a display device 30 such as a display screen orcomputer monitor. NOC video adapter 26 is connected to processor 12through a high speed video bus 32, bus adapter 18, and the front sidebus 34, which is also a high speed bus. NOC Coprocessor 28 is connectedto processor 12 through bus adapter 18, and front side buses 34 and 36,which is also a high speed bus. The NOC coprocessor of FIG. 1 may beoptimized, for example, to accelerate particular data processing tasksat the behest of the main processor 12.

The exemplary NOC video adapter 26 and NOC coprocessor 28 of FIG. 1 eachinclude a NOC, including integrated processor (‘IP’) blocks, routers,memory communications controllers, and network interface controllers,the details of which will be discussed in greater detail below inconnection with FIGS. 2-3. The NOC video adapter and NOC coprocessor areeach optimized for programs that use parallel processing and alsorequire fast random access to shared memory. It will be appreciated byone of ordinary skill in the art having the benefit of the instantdisclosure, however, that the invention may be implemented in devicesand device architectures other than NOC devices and devicearchitectures. The invention is therefore not limited to implementationwithin an NOC device.

Computer 10 of FIG. 1 includes disk drive adapter 38 coupled through anexpansion bus 40 and bus adapter 18 to processor 12 and other componentsof the computer 10. Disk drive adapter 38 connects non-volatile datastorage to the computer 10 in the form of disk drive 24, and may beimplemented, for example, using Integrated Drive Electronics (‘IDE’)adapters, Small Computer System Interface (‘SCSI’) adapters, and othersas will occur to those of skill in the art. Non-volatile computer memoryalso may be implemented for as an optical disk drive, electricallyerasable programmable read-only memory (so-called ‘EEPROM’ or ‘Flash’memory), RAM drives, and so on, as will occur to those of skill in theart.

Computer 10 also includes one or more input/output (‘I/O’) adapters 42,which implement user-oriented input/output through, for example,software drivers and computer hardware for controlling output to displaydevices such as computer display screens, as well as user input fromuser input devices 44 such as keyboards and mice. In addition, computer10 includes a communications adapter 46 for data communications withother computers 48 and for data communications with a datacommunications network 50. Such data communications may be carried outserially through RS-232 connections, through external buses such as aUniversal Serial Bus (‘USB’), through data communications datacommunications networks such as IP data communications networks, and inother ways as will occur to those of skill in the art. Communicationsadapters implement the hardware level of data communications throughwhich one computer sends data communications to another computer,directly or through a data communications network. Examples ofcommunications adapters suitable for use in computer 10 include modemsfor wired dial-up communications, Ethernet (IEEE 802.3) adapters forwired data communications network communications, and 802.11 adaptersfor wireless data communications network communications.

For further explanation, FIG. 2 sets forth a functional block diagram ofan example NOC 102 according to embodiments of the present invention.The NOC in FIG. 2 is implemented on a ‘chip’ 100, that is, on anintegrated circuit. NOC 102 includes integrated processor (‘IP’) blocks104, routers 110, memory communications controllers 106, and networkinterface controllers 108 grouped into interconnected nodes. Each IPblock 104 is adapted to a router 110 through a memory communicationscontroller 106 and a network interface controller 108. Each memorycommunications controller controls communications between an IP blockand memory, and each network interface controller 108 controls inter-IPblock communications through routers 110.

In NOC 102, each IP block represents a reusable unit of synchronous orasynchronous logic design used as a building block for data processingwithin the NOC. The term ‘IP block’ is sometimes expanded as‘intellectual property block,’ effectively designating an IP block as adesign that is owned by a party, that is the intellectual property of aparty, to be licensed to other users or designers of semiconductorcircuits. In the scope of the present invention, however, there is norequirement that IP blocks be subject to any particular ownership, sothe term is always expanded in this specification as ‘integratedprocessor block.’ IP blocks, as specified here, are reusable units oflogic, cell, or chip layout design that may or may not be the subject ofintellectual property. IP blocks are logic cores that can be formed asASIC chip designs or FPGA logic designs.

One way to describe IP blocks by analogy is that IP blocks are for NOCdesign what a library is for computer programming or a discreteintegrated circuit component is for printed circuit board design. InNOCs consistent with embodiments of the present invention, IP blocks maybe implemented as generic gate netlists, as complete special purpose orgeneral purpose microprocessors, or in other ways as may occur to thoseof skill in the art. A netlist is a Boolean-algebra representation(gates, standard cells) of an IP block's logical-function, analogous toan assembly-code listing for a high-level program application. NOCs alsomay be implemented, for example, in synthesizable form, described in ahardware description language such as Verilog or VHDL. In addition tonetlist and synthesizable implementation, NOCs also may be delivered inlower-level, physical descriptions. Analog IP block elements such asSERDES, PLL, DAC, ADC, and so on, may be distributed in atransistor-layout format such as GDSII. Digital elements of IP blocksare sometimes offered in layout format as well. It will also beappreciated that IP blocks, as well as other logic circuitry implementedconsistent with the invention may be distributed in the form of computerdata files, e.g., logic definition program code, that define at variouslevels of detail the functionality and/or layout of the circuitarrangements implementing such logic. Thus, while the invention has andhereinafter will be described in the context of circuit arrangementsimplemented in fully functioning integrated circuit devices and dataprocessing systems utilizing such devices, those of ordinary skill inthe art having the benefit of the instant disclosure will appreciatethat circuit arrangements consistent with the invention are capable ofbeing distributed as program products in a variety of forms, and thatthe invention applies equally regardless of the particular type ofcomputer readable or signal bearing media being used to actually carryout the distribution. Examples of computer readable or signal bearingmedia include, but are not limited to, physical, recordable type mediasuch as volatile and non-volatile memory devices, floppy disks, harddisk drives, CD-ROMs, and DVDs (among others), and transmission typemedia such as digital and analog communication links.

Each IP block 104 in the example of FIG. 2 is adapted to a router 110through a memory communications controller 106. Each memorycommunication controller is an aggregation of synchronous andasynchronous logic circuitry adapted to provide data communicationsbetween an IP block and memory. Examples of such communications betweenIP blocks and memory include memory load instructions and memory storeinstructions. The memory communications controllers 106 are described inmore detail below with reference to FIG. 3. Each IP block 104 is alsoadapted to a router 110 through a network interface controller 108,which controls communications through routers 110 between IP blocks 104.Examples of communications between IP blocks include messages carryingdata and instructions for processing the data among IP blocks inparallel applications and in pipelined applications. The networkinterface controllers 108 are also described in more detail below withreference to FIG. 3.

Routers 110, and the corresponding links 118 therebetween, implement thenetwork operations of the NOC. The links 118 may be packet structuresimplemented on physical, parallel wire buses connecting all the routers.That is, each link may be implemented on a wire bus wide enough toaccommodate simultaneously an entire data switching packet, includingall header information and payload data. If a packet structure includes64 bytes, for example, including an eight byte header and 56 bytes ofpayload data, then the wire bus subtending each link is 64 bytes wide,512 wires. In addition, each link may be bidirectional, so that if thelink packet structure includes 64 bytes, the wire bus actually contains1024 wires between each router and each of its neighbors in the network.In such an implementation, a message could include more than one packet,but each packet would fit precisely onto the width of the wire bus. Inthe alternative, a link may be implemented on a wire bus that is onlywide enough to accommodate a portion of a packet, such that a packetwould be broken up into multiple beats, e.g., so that if a link isimplemented as 16 bytes in width, or 128 wires, a 64 byte packet couldbe broken into four beats. It will be appreciated that differentimplementations may used different bus widths based on practicalphysical limits as well as desired performance characteristics. If theconnection between the router and each section of wire bus is referredto as a port, then each router includes five ports, one for each of fourdirections of data transmission on the network and a fifth port foradapting the router to a particular IP block through a memorycommunications controller and a network interface controller.

Each memory communications controller 106 controls communicationsbetween an IP block and memory. Memory can include off-chip main RAM112, memory 114 connected directly to an IP block through a memorycommunications controller 106, on-chip memory enabled as an IP block116, and on-chip caches. In NOC 102, either of the on-chip memories 114,116, for example, may be implemented as on-chip cache memory. All theseforms of memory can be disposed in the same address space, physicaladdresses or virtual addresses, true even for the memory attacheddirectly to an IP block. Memory addressed messages therefore can beentirely bidirectional with respect to IP blocks, because such memorycan be addressed directly from any IP block anywhere on the network.Memory 116 on an IP block can be addressed from that IP block or fromany other IP block in the NOC. Memory 114 attached directly to a memorycommunication controller can be addressed by the IP block that isadapted to the network by that memory communication controller—and canalso be addressed from any other IP block anywhere in the NOC.

NOC 102 includes two memory management units (‘MMUs’) 120, 122,illustrating two alternative memory architectures for NOCs consistentwith embodiments of the present invention. MMU 120 is implemented withinan IP block, allowing a processor within the IP block to operate invirtual memory while allowing the entire remaining architecture of theNOC to operate in a physical memory address space. MMU 122 isimplemented off-chip, connected to the NOC through a data communicationsport 124. The port 124 includes the pins and other interconnectionsrequired to conduct signals between the NOC and the MMU, as well assufficient intelligence to convert message packets from the NOC packetformat to the bus format required by the external MMU 122. The externallocation of the MMU means that all processors in all IP blocks of theNOC can operate in virtual memory address space, with all conversions tophysical addresses of the off-chip memory handled by the off-chip MMU122.

In addition to the two memory architectures illustrated by use of theMMUs 120, 122, data communications port 126 illustrates a third memoryarchitecture useful in NOCs capable of being utilized in embodiments ofthe present invention. Port 126 provides a direct connection between anIP block 104 of the NOC 102 and off-chip memory 112. With no MMU in theprocessing path, this architecture provides utilization of a physicaladdress space by all the IP blocks of the NOC. In sharing the addressspace bi-directionally, all the IP blocks of the NOC can access memoryin the address space by memory-addressed messages, including loads andstores, directed through the IP block connected directly to the port126. The port 126 includes the pins and other interconnections requiredto conduct signals between the NOC and the off-chip memory 112, as wellas sufficient intelligence to convert message packets from the NOCpacket format to the bus format required by the off-chip memory 112.

In the example of FIG. 2, one of the IP blocks is designated a hostinterface processor 128. A host interface processor 128 provides aninterface between the NOC and a host computer 10 in which the NOC may beinstalled and also provides data processing services to the other IPblocks on the NOC, including, for example, receiving and dispatchingamong the IP blocks of the NOC data processing requests from the hostcomputer. A NOC may, for example, implement a video graphics adapter 26or a coprocessor 28 on a larger computer 10 as described above withreference to FIG. 1. In the example of FIG. 2, the host interfaceprocessor 128 is connected to the larger host computer through a datacommunications port 130. The port 130 includes the pins and otherinterconnections required to conduct signals between the NOC and thehost computer, as well as sufficient intelligence to convert messagepackets from the NOC to the bus format required by the host computer 10.In the example of the NOC coprocessor in the computer of FIG. 1, such aport would provide data communications format translation between thelink structure of the NOC coprocessor 28 and the protocol required forthe front side bus 36 between the NOC coprocessor 28 and the bus adapter18.

FIG. 3 next illustrates a functional block diagram illustrating ingreater detail the components implemented within an IP block 104, memorycommunications controller 106, network interface controller 108 androuter 110 in NOC 102, collectively illustrated at 132. IP block 104includes a computer processor 134 and I/O functionality 136. In thisexample, computer memory is represented by a segment of random accessmemory (‘RAM’) 138 in IP block 104. The memory, as described above withreference to FIG. 2, can occupy segments of a physical address spacewhose contents on each IP block are addressable and accessible from anyIP block in the NOC. The processors 134, I/O capabilities 136, andmemory 138 in each IP block effectively implement the IP blocks asgenerally programmable microcomputers. As explained above, however, inthe scope of the present invention, IP blocks generally representreusable units of synchronous or asynchronous logic used as buildingblocks for data processing within a NOC. Implementing IP blocks asgenerally programmable microcomputers, therefore, although a commonembodiment useful for purposes of explanation, is not a limitation ofthe present invention.

In NOC 102 of FIG. 3, each memory communications controller 106 includesa plurality of memory communications execution engines 140. Each memorycommunications execution engine 140 is enabled to execute memorycommunications instructions from an IP block 104, includingbidirectional memory communications instruction flow 141, 142, 144between the network and the IP block 104. The memory communicationsinstructions executed by the memory communications controller mayoriginate, not only from the IP block adapted to a router through aparticular memory communications controller, but also from any IP block104 anywhere in NOC 102. That is, any IP block in the NOC can generate amemory communications instruction and transmit that memorycommunications instruction through the routers of the NOC to anothermemory communications controller associated with another IP block forexecution of that memory communications instruction. Such memorycommunications instructions can include, for example, translationlookaside buffer control instructions, cache control instructions,barrier instructions, and memory load and store instructions.

Each memory communications execution engine 140 is enabled to execute acomplete memory communications instruction separately and in parallelwith other memory communications execution engines. The memorycommunications execution engines implement a scalable memory transactionprocessor optimized for concurrent throughput of memory communicationsinstructions. Memory communications controller 106 supports multiplememory communications execution engines 140 all of which runconcurrently for simultaneous execution of multiple memorycommunications instructions. A new memory communications instruction isallocated by the memory communications controller 106 to a memorycommunications engine 140 and memory communications execution engines140 can accept multiple response events simultaneously. In this example,all of the memory communications execution engines 140 are identical.Scaling the number of memory communications instructions that can behandled simultaneously by a memory communications controller 106,therefore, is implemented by scaling the number of memory communicationsexecution engines 140.

In NOC 102 of FIG. 3, each network interface controller 108 is enabledto convert communications instructions from command format to networkpacket format for transmission among the IP blocks 104 through routers110. The communications instructions may be formulated in command formatby the IP block 104 or by memory communications controller 106 andprovided to the network interface controller 108 in command format. Thecommand format may be a native format that conforms to architecturalregister files of IP block 104 and memory communications controller 106.The network packet format is typically the format required fortransmission through routers 110 of the network. Each such message iscomposed of one or more network packets. Examples of such communicationsinstructions that are converted from command format to packet format inthe network interface controller include memory load instructions andmemory store instructions between IP blocks and memory. Suchcommunications instructions may also include communications instructionsthat send messages among IP blocks carrying data and instructions forprocessing the data among IP blocks in parallel applications and inpipelined applications.

In NOC 102 of FIG. 3, each IP block is enabled to sendmemory-address-based communications to and from memory through the IPblock's memory communications controller and then also through itsnetwork interface controller to the network. A memory-address-basedcommunications is a memory access instruction, such as a loadinstruction or a store instruction, that is executed by a memorycommunication execution engine of a memory communications controller ofan IP block. Such memory-address-based communications typicallyoriginate in an IP block, formulated in command format, and handed offto a memory communications controller for execution.

Many memory-address-based communications are executed with messagetraffic, because any memory to be accessed may be located anywhere inthe physical memory address space, on-chip or off-chip, directlyattached to any memory communications controller in the NOC, orultimately accessed through any IP block of the NOC—regardless of whichIP block originated any particular memory-address-based communication.Thus, in NOC 102, all memory-address-based communications that areexecuted with message traffic are passed from the memory communicationscontroller to an associated network interface controller for conversionfrom command format to packet format and transmission through thenetwork in a message. In converting to packet format, the networkinterface controller also identifies a network address for the packet independence upon the memory address or addresses to be accessed by amemory-address-based communication. Memory address based messages areaddressed with memory addresses. Each memory address is mapped by thenetwork interface controllers to a network address, typically thenetwork location of a memory communications controller responsible forsome range of physical memory addresses. The network location of amemory communication controller 106 is naturally also the networklocation of that memory communication controller's associated router110, network interface controller 108, and IP block 104. The instructionconversion logic 150 within each network interface controller is capableof converting memory addresses to network addresses for purposes oftransmitting memory-address-based communications through routers of aNOC.

Upon receiving message traffic from routers 110 of the network, eachnetwork interface controller 108 inspects each packet for memoryinstructions. Each packet containing a memory instruction is handed tothe memory communications controller 106 associated with the receivingnetwork interface controller, which executes the memory instructionbefore sending the remaining payload of the packet to the IP block forfurther processing. In this way, memory contents are always prepared tosupport data processing by an IP block before the IP block beginsexecution of instructions from a message that depend upon particularmemory content.

In NOC 102 of FIG. 3, each IP block 104 is enabled to bypass its memorycommunications controller 106 and send inter-IP block, network-addressedcommunications 146 directly to the network through the IP block'snetwork interface controller 108. Network-addressed communications aremessages directed by a network address to another IP block. Suchmessages transmit working data in pipelined applications, multiple datafor single program processing among IP blocks in a SIMD application, andso on, as will occur to those of skill in the art. Such messages aredistinct from memory-address-based communications in that they arenetwork addressed from the start, by the originating IP block whichknows the network address to which the message is to be directed throughrouters of the NOC. Such network-addressed communications are passed bythe IP block through I/O functions 136 directly to the IP block'snetwork interface controller in command format, then converted to packetformat by the network interface controller and transmitted throughrouters of the NOC to another IP block. Such network-addressedcommunications 146 are bi-directional, potentially proceeding to andfrom each IP block of the NOC, depending on their use in any particularapplication. Each network interface controller, however, is enabled toboth send and receive such communications to and from an associatedrouter, and each network interface controller is enabled to both sendand receive such communications directly to and from an associated IPblock, bypassing an associated memory communications controller 106.

Each network interface controller 108 in the example of FIG. 3 is alsoenabled to implement virtual channels on the network, characterizingnetwork packets by type. Each network interface controller 108 includesvirtual channel implementation logic 148 that classifies eachcommunication instruction by type and records the type of instruction ina field of the network packet format before handing off the instructionin packet form to a router 110 for transmission on the NOC. Examples ofcommunication instruction types include inter-IP blocknetwork-address-based messages, request messages, responses to requestmessages, invalidate messages directed to caches; memory load and storemessages; and responses to memory load messages, etc.

Each router 110 in the example of FIG. 3 includes routing logic 152,virtual channel control logic 154, and virtual channel buffers 156. Therouting logic typically is implemented as a network of synchronous andasynchronous logic that implements a data communications protocol stackfor data communication in the network formed by the routers 110, links118, and bus wires among the routers. Routing logic 152 includes thefunctionality that readers of skill in the art might associate inoff-chip networks with routing tables, routing tables in at least someembodiments being considered too slow and cumbersome for use in a NOC.Routing logic implemented as a network of synchronous and asynchronouslogic can be configured to make routing decisions as fast as a singleclock cycle. The routing logic in this example routes packets byselecting a port for forwarding each packet received in a router. Eachpacket contains a network address to which the packet is to be routed.

In describing memory-address-based communications above, each memoryaddress was described as mapped by network interface controllers to anetwork address, a network location of a memory communicationscontroller. The network location of a memory communication controller106 is naturally also the network location of that memory communicationcontroller's associated router 110, network interface controller 108,and IP block 104. In inter-IP block, or network-address-basedcommunications, therefore, it is also typical for application-level dataprocessing to view network addresses as the location of an IP blockwithin the network formed by the routers, links, and bus wires of theNOC. FIG. 2 illustrates that one organization of such a network is amesh of rows and columns in which each network address can beimplemented, for example, as either a unique identifier for each set ofassociated router, IP block, memory communications controller, andnetwork interface controller of the mesh or x, y coordinates of eachsuch set in the mesh.

In NOC 102 of FIG. 3, each router 110 implements two or more virtualcommunications channels, where each virtual communications channel ischaracterized by a communication type. Communication instruction types,and therefore virtual channel types, include those mentioned above:inter-IP block network-address-based messages, request messages,responses to request messages, invalidate messages directed to caches;memory load and store messages; and responses to memory load messages,and so on. In support of virtual channels, each router 110 in theexample of FIG. 3 also includes virtual channel control logic 154 andvirtual channel buffers 156. The virtual channel control logic 154examines each received packet for its assigned communications type andplaces each packet in an outgoing virtual channel buffer for thatcommunications type for transmission through a port to a neighboringrouter on the NOC.

Each virtual channel buffer 156 has finite storage space. When manypackets are received in a short period of time, a virtual channel buffercan fill up—so that no more packets can be put in the buffer. In otherprotocols, packets arriving on a virtual channel whose buffer is fullwould be dropped. Each virtual channel buffer 156 in this example,however, is enabled with control signals of the bus wires to advisesurrounding routers through the virtual channel control logic to suspendtransmission in a virtual channel, that is, suspend transmission ofpackets of a particular communications type. When one virtual channel isso suspended, all other virtual channels are unaffected—and can continueto operate at full capacity. The control signals are wired all the wayback through each router to each router's associated network interfacecontroller 108. Each network interface controller is configured to, uponreceipt of such a signal, refuse to accept, from its associated memorycommunications controller 106 or from its associated IP block 104,communications instructions for the suspended virtual channel. In thisway, suspension of a virtual channel affects all the hardware thatimplements the virtual channel, all the way back up to the originatingIP blocks.

One effect of suspending packet transmissions in a virtual channel isthat no packets are ever dropped. When a router encounters a situationin which a packet might be dropped in some unreliable protocol such as,for example, the Internet Protocol, the routers in the example of FIG. 3may suspend by their virtual channel buffers 156 and their virtualchannel control logic 154 all transmissions of packets in a virtualchannel until buffer space is again available, eliminating any need todrop packets. The NOC of FIG. 3, therefore, may implement highlyreliable network communications protocols with an extremely thin layerof hardware.

The example NOC of FIG. 3 may also be configured to maintain cachecoherency between both on-chip and off-chip memory caches. Each NOC cansupport multiple caches each of which operates against the sameunderlying memory address space. For example, caches may be controlledby IP blocks, by memory communications controllers, or by cachecontrollers external to the NOC. Either of the on-chip memories 114, 116in the example of FIG. 2 may also be implemented as an on-chip cache,and, within the scope of the present invention, cache memory can beimplemented off-chip also.

Each router 110 illustrated in FIG. 3 includes five ports, four ports158A-D connected through bus wires 118 to other routers and a fifth port160 connecting each router to its associated IP block 104 through anetwork interface controller 108 and a memory communications controller106. As can be seen from the illustrations in FIGS. 2 and 3, the routers110 and the links 118 of the NOC 102 form a mesh network with verticaland horizontal links connecting vertical and horizontal ports in eachrouter. In the illustration of FIG. 3, for example, ports 158A, 158C and160 are termed vertical ports, and ports 158B and 158D are termedhorizontal ports.

FIG. 4 next illustrates in another manner one exemplary implementationof an IP block 104 consistent with the invention, implemented as aprocessing element partitioned into an instruction unit (IU) 162,execution unit (XU) 164 and auxiliary execution unit (AXU) 166. In theillustrated implementation, IU 162 includes a plurality of instructionbuffers 168 that receive instructions from an L1 instruction cache(iCACHE) 170. Each instruction buffer 168 is dedicated to one of aplurality, e.g., four, symmetric multithreaded (SMT) hardware threads.An effective-to-real translation unit (iERAT) 172 is coupled to iCACHE170, and is used to translate instruction fetch requests from aplurality of thread fetch sequencers 174 into real addresses forretrieval of instructions from lower order memory. Each thread fetchsequencer 174 is dedicated to a particular hardware thread, and is usedto ensure that instructions to be executed by the associated thread isfetched into the iCACHE for dispatch to the appropriate execution unit.As also shown in FIG. 4, instructions fetched into instruction buffer168 may also be monitored by branch prediction logic 176, which provideshints to each thread fetch sequencer 174 to minimize instruction cachemisses resulting from branches in executing threads.

IU 162 also includes a dependency/issue logic block 178 dedicated toeach hardware thread, and configured to resolve dependencies and controlthe issue of instructions from instruction buffer 168 to XU 164. Inaddition, in the illustrated embodiment, separate dependency/issue logic180 is provided in AXU 166, thus enabling separate instructions to beconcurrently issued by different threads to XU 164 and AXU 166. In analternative embodiment, logic 180 may be disposed in IU 162, or may beomitted in its entirety, such that logic 178 issues instructions to AXU166.

XU 164 is implemented as a fixed point execution unit, including a setof general purpose registers (GPR's) 182 coupled to fixed point logic184, branch logic 186 and load/store logic 188. Load/store logic 188 iscoupled to an L1 data cache (dCACHE) 190, with effective to realtranslation provided by dERAT logic 192. XU 164 may be configured toimplement practically any instruction set, e.g., all or a portion of a32 b or 64 b PowerPC instruction set.

AXU 166 operates as an auxiliary execution unit including dedicateddependency/issue logic 180 along with one or more execution blocks 194.AXU 166 may include any number of execution blocks, and may implementpractically any type of execution unit, e.g., a floating point unit, orone or more specialized execution units such as encryption/decryptionunits, coprocessors, vector processing units, graphics processing units,XML processing units, etc. In the illustrated embodiment, AXU 166includes a high speed auxiliary interface to XU 164, e.g., to supportdirect moves between AXU architected state and XU architected state.

Communication with IP block 104 may be managed in the manner discussedabove in connection with FIG. 2, via network interface controller 108coupled to NOC 102. Address-based communication, e.g., to access L2cache memory, may be provided, along with message-based communication.For example, each IP block 104 may include a dedicated in box and/or outbox in order to handle inter-node communications between IP blocks.

Embodiments of the present invention may be implemented within thehardware and software environment described above in connection withFIGS. 1-4. However, it will be appreciated by one of ordinary skill inthe art having the benefit of the instant disclosure that the inventionmay be implemented in a multitude of different environments, and thatother modifications may be made to the aforementioned hardware andsoftware embodiment without departing from the spirit and scope of theinvention. As such, the invention is not limited to the particularhardware and software environment disclosed herein.

Instruction-Based Persistent Multiplexer Control of Vector-BasedExecution Unit

Turning now to FIG. 5, this figure illustrates an exemplary processingunit 200 capable of performing instruction-based persistent multiplexercontrol consistent with the invention. Processing unit 200 includes anissue unit 202 coupled to a vector unit 204 (also referred to herein asa vector-based execution unit), and may be implemented, for example, inan IP block such as an IP block 104 from FIGS. 1-4. In the alternative,processing unit 200 may be implemented in other processor architecturesthat issue and execute instructions, including single or multi-coremicroprocessors or microcontrollers.

Issue unit 202 is a multithreaded issue unit capable of receivinginstructions from multiple (N) threads 206. Issue select logic 208operates to schedule the issuance of instructions by the variousthreads, and issue unit 202 typically includes logic for managingdependencies between instructions, in a manner generally understood inthe art. Issue select logic 208 outputs instructions to vector unit 204,which causes the vector unit to initiate execution of receivedinstructions.

Vector unit 204 includes a register file 210 coupled to an executionpipeline 212. Register file 210 includes an array of vector registers,each of which including a plurality of words. For example, register file210 may be implemented to support 4(quad)word vectors with 32 b-widewords, with 128 quadword (128 b) vector registers. The 128 vectorregisters may be shared by threads 206, or in the alternative, may bepartitioned to different threads, e.g., to provide each thread with adedicated set of registers. Thus, for example, if four threads 206 aresupported, register 210 may be organized to provide 32 128 b vectorregisters to each thread 206. It will be appreciated that differentnumbers of registers, partitions, words per vector and bits per word maybe supported in different embodiments.

Execution pipeline 211, in response to instructions received from issueunit 202, performs mathematical, logical or other operations on one ormore source operand vectors retrieved from selected vector registers inregister file 210. For example, execution pipeline 211 may receive up tothree source or operand vectors from register file 210, denoted assource operand vectors SrcA, SrcB and SrC in FIG. 5, and may storeresult data back into register file 210, e.g., in the form of a targetvector written to a selected vector register in the register file.Execution pipeline 211 may include, for example, a plurality ofprocessing lanes or sub-units capable of performing similar operationson different words of one or more operand vectors in parallel. Forexample, in the illustrated embodiment, if 4 word vectors are supported,execution pipeline 211 may include 4 processing lanes to process the 4words of each vector in parallel. Vector unit 204 may be implemented asa number of different types of execution units, e.g., floating pointunits, fixed point units, or specialized execution units such asgraphics processing units, encryption/decryption units, coprocessors,XML processing units, etc.

To implement instruction-based persistent multiplexer control, swizzlelogic including swizzle control logic block 212, storage elements 214and multiplexer logic blocks 216 is utilized in processing unit 200.Swizzle control logic block 212 is responsive to persistent swizzleinstructions processed by issue select logic 208 to store stateinformation in a plurality of thread-specific storage elements, orswizzle control latches, 214. The persisted state information is thenfed to a plurality of multiplexer logic blocks 216 to selectivelyshuffle the words in operand vectors retrieved by vector unit 204 fromregister file 210. In the illustrated implementation, execution pipeline210 is a multiply-add floating point pipeline that processes threeoperand vectors, denoted source vectors A, B and C, and the words ineach source vector are passed to separate multiplexer logic blocks 216.

Within each multiplexer logic block 216 is an input latch 218, a set ofmultiplexers 220 and an output latch 222. For an N-word vector, N-wordlatches 218, 222 are used, as are N multiplexers 220. Each multiplexer220 includes an output coupled to a respective word in output latch 220,as well as includes N inputs such that each word of the input latch 218is fed to each multiplexer 220. Thus, with quad(4)word operand vectors,each latch 218, 220 includes storage for four words, and four 4-inputmultiplexers 220 are coupled between the latches.

Multiplexer select signals are provided by swizzle control logic 212 tocontrol the routing of each word in the input latch 218 to a particularword in the output latch 222. While in the illustrated embodiment eachword in the input latch is routed to one of the words in the outputlatch, in some embodiments particular words in the input latch may beduplicated and routed to multiple words of the output latch, wherebysome words in the input latch may not be routed to any word of theoutput latch.

Multiplexers 220 function as word swapping multiplexers at the top ofthe arithmetic pipe described above, while swizzle control logic 212functions as a state machine that, responsive to a persistent swizzleinstruction, sets the multiplexer control state for each multiplexer 220that remains constant until another persistent swizzle instruction setsthe state to something else, or until a flush occurs. In a multithreadedarchitecture such as shown in FIG. 5, for each thread in the processingunit, a separate swizzle control latch 214 is provided so that themultiplexers 220 are updated with the state information for theappropriate thread whenever an instruction from that thread is currentlybeing executed in the vector unit 204.

In the illustrated embodiment, the default state information stored ineach swizzle control latch 214, which is reset on power up, is thenatural order of words in the quadword, i.e., for words x, y, z, w in anoperand vector, the order x, y, z, w will be output from latch 216. If apersistent swizzle instruction has been issued from a particular threadand its associated swizzle control latches have been set with the datafrom that instruction, and following that an arithmetic instruction froma different thread is issued, that arithmetic instruction will use thestate information associated with its own thread, not that of the mostrecently issued persistent swizzle instruction. If an arithmeticinstruction is issued but no persistent swizzle instruction has beenissued previously for that thread, the natural word order will be used.

In the illustrated embodiment, a persistent swizzle instruction mayoccupy the same amount of instruction memory as other instructions inthe instruction set for the processing unit, e.g., 32 bits in aprocessing unit that processes 32 bit arithmetic instructions.Furthermore, a persistent swizzle instruction may be handled like anormal instruction during instruction caching, buffering, dependencystalling and issue. In the illustrated embodiment, at issue time, issueselect logic 208 sets the state information in the associated swizzlecontrol latch 214 for the thread, but the persistent swizzle instructionis not required to continue down the arithmetic pipeline or otherwiseoccupy a pipeline stage, such that an arithmetic instruction dependenton the swizzle may be issued very soon after its associated persistentswizzle instruction, compared to dependent arithmetic instructions.

FIG. 6, for example, illustrates an exemplary instruction format for apersistent swizzle instruction 230 consistent with the invention. Inthis implementation, instruction 230 includes a primary opcode field 232and secondary opcode field 234 to respectively represent the primary andsecondary opcodes for the instruction. A plurality of operand vectorfields 236 (e.g., one each for the A, B and C operand vectors) areprovided in the instruction, with each operand vector field 236including a plurality of control bits that selectively shuffle each ofthe plurality of words in each operand vector. For example, each operandvector field 236 may includes a plurality of word-specific fields 238that define the state information to be stored for each operand vector.In one embodiment, where each operand vector has N words, each operandvector field includes N word-specific fields, with each word-specificfield including log₂N bits that specify to which of N words each wordshould be shuffled. Consequently, for quad(4)word operand vectors, eachoperand vector field 236 may be 8 bits in length, composed of fourword-specific fields of 2 bits each. The 2 bits per word-specific fieldare capable of routing a word from an operand vector to one of fourpossible words in the output latch.

FIG. 7 illustrates at 240 an exemplary sequence of operations performedby processing unit 200 in processing instructions from an instructionstream. Upon receipt of an incoming instruction, a determination is madein block 242 as to whether the instruction is valid. If not, no furtherprocessing of the instruction is performed, and an error condition mayoptionally be signaled.

If the instruction is valid, however, control passes to block 244 todetermine whether the instruction is a persistent swizzle instruction.If not, indicating that the instruction is an arithmetic instruction forexecution by vector unit 204, control passes to block 246 to performoperand word reordering according to the contents of the swizzle controllatch 214 for the associated thread. Control then passes to block 248 toperform the arithmetic operation requested by the instruction, and withthe operand vectors reordered as specified in the swizzle control latch214 for the thread. Processing of the instruction is complete.

Returning to block 244, if the instruction is a persistent swizzleinstruction, control passes to block 250 to update the swizzle controllatch 214 for the current thread, using the state information stored inthe instruction. Processing of the instruction is then complete.

In addition, as shown in block 252, it may also be desirable in somecircumstances to additionally take a snapshot of the current state ofthe processing unit in association with processing the persistentswizzle instruction. Particularly when each swizzle control latch 214 isnot software accessible, flush operations that may be performed willtypically require that a rollback occur to the last persistent swizzleinstruction whenever the state is restored, to ensure that the stateinformation for the persistent swizzle instruction can be restored priorto execution of any subsequent instructions that rely on that stateinformation.

Thus, for example, if a flush occurs due to a asynchronous interrupt (orany other flush reason) the state machine implemented in swizzle controllogic 212 and the swizzle control latches 214 are reset to defaultstate, and after the interrupt handler execution has completed, theprocessing unit resumes execution at or before the last persistentswizzle instruction to ensure that the persistent swizzle instructionthat is associated with particular arithmetic instructions alwaysretains that association. Furthermore, where the persistent swizzleinstruction does not directly update any architected state that can beread by any software instructions, and no completed execution isreported to the flush control processing unit logic, the processing unitcan typically be relied upon to always re-issue the persistent swizzleinstruction after it has been flushed without encountering unpredictableresults. Thus, as shown in FIG. 8, during the performance of a flushoperation 260, the current state is saved at block 262, the state isrestored to a point prior to the last swizzle instruction in block 264,and execution is restarted from (or before) the last persistent swizzleinstruction in block 266.

In the implementation illustrated in FIGS. 5-8, a set of swizzle controllatches, which are desirably not software accessible, are used tocontrol the multiplexers for the purpose of instruction-based persistentmultiplexer control. In alternate embodiments, however, it may bedesirable to use software-accessible special purpose registers to storestate information in lieu of non-accessible storage elements. FIG. 9,for example, illustrates an alternate processing unit 300, whichincludes an issue unit 302 coupled to a vector unit 304, which arerespectively similar in configuration to issue unit 202 and vector unit204 of processing unit 200 (FIG. 5). Issue unit 302 is a multithreadedissue unit capable of receiving instructions from multiple (N) threads306, with issue select logic 308 used to schedule the issuance ofinstructions by the various threads. Vector unit 304 includes a registerfile 310 coupled to an execution pipeline 311.

To implement instruction-based persistent multiplexer control, swizzlelogic includes a swizzle control logic block 312 and multiplexer logicblocks 316, the latter of which are similarly configured as multiplexerlogic blocks 216 of processing unit 200. However, rather thannon-accessible storage elements, the swizzle logic in processing unit300 includes a special purpose register (SPR) file array 314 withinwhich is stored a set of software-accessible swizzle SPR's that havebeen architected into processing unit 300.

The swizzle SPR's in SPR file array 314 typically store the same type ofinformation as is stored in the swizzle control latches 214 ofprocessing unit 200. However, the accessibility of the SPR's to softwareprovide an advantage in terms of ease of configurability and facilitatethe handling of flush conditions. Specifically, the software accessiblenature of the SPR's may allow for the multiplexer control state to besaved and restored by instructions in an interrupt handler, whichenables flush conditions to be handled safely. In such an embodiment,the state is persistent and consistent with the contents of the specialpurpose register until a flush occurs. After a flush, such as in thecase of a timer interrupt to allow for time slice scheduling of multipleprocesses in an operating system, the multiplexer control behavior andthe contents of the special purpose register will still be persistentand consistent, but the interrupt handler may save the contents of thespecial purpose register out to memory, so that the thread's state canbe restored for proper operation later on. In addition, if the interrupthandler requires the use of vector instructions, the interrupt handlermay need to set the contents of the swizzle special purpose registerappropriately.

The swizzle SPR's 314 and the state machine for the swizzle logic may bedisposed in different regions or components of a processing unit indifferent embodiments of the invention. For example, FIG. 10 illustratesan exemplary processing unit 330 similar to that implemented in IP block104 of FIG. 4, incorporating a primary processing unit 332 coupled to anauxiliary execution unit (AXU) 334.

Primary processing unit 332 may include an issue unit 336 and anexecution unit (XU) implemented as a fixed point execution unit 338. XU338 is architected to include a set of general purpose registers (GPR's)340 as well as a set of special purpose registers (SPR's) 342, of whichseveral may be allocated as swizzle SPR's 343. AXU 334 operates as avector floating point execution unit including a dedicated issue unit344 and a vector unit 346, including a set of vector registers (VR's)348 forming a register file for the vector unit.

To implement instruction-based multiplexer control, a set of swizzlemultiplexers 350, configured in a similar manner to multiplexers 316 ofprocessing unit 300, are disposed in the execution pipeline of vectorunit 346. However, as shown in FIG. 10, both the swizzle SPR's 343 andat least a portion of the swizzle control logic 352 are disposedexternally to AXU 334, and are logically incorporated into primaryprocessing unit 332. A communications path 354 between swizzle SPR's 343and swizzle multiplexers 350 is defined such that the state informationmaintained in the SPR's can be used to control the word ordering used bythe AXU vector unit. By locating the SPR's and at least a portion of theswizzle control logic in primary processing unit 332, saves and restoresof the SPR's during context switching operations is typicallyfacilitated.

On the other hand, it may be desirable in other embodiments to locatethe swizzle SPR's and the bulk of the swizzle control logic in the AXUitself. FIG. 11, for example, illustrates an exemplary processing unit360 similar to processing unit 330, incorporating a primary processingunit 362 coupled to an auxiliary execution unit (AXU) 364. Primaryprocessing unit 362 may include an issue unit 366 and an execution unit(XU) implemented as a fixed point execution unit 368. XU 368 isarchitected to include a set of general purpose registers (GPR's) 370 aswell as a set of special purpose registers (SPR's) 372. However, unlikeprocessing unit 330, the swizzle SPR's in processing unit 360 aredisposed in AXU 364 (block 374).

AXU 364 operates as a vector floating point execution unit including adedicated issue unit 376 and a vector unit 378, including a set ofvector registers (VR's) 380 forming a register file for the vector unit.To implement instruction-based multiplexer control in this embodiment, aset of swizzle multiplexers 382, configured in a similar manner tomultiplexers 316 of processing unit 300, are disposed in the executionpipeline of vector unit 378. In addition, the swizzle SPR's 374 and theswizzle control logic 384 are disposed within the AXU 364, thuslocalizing the swizzle functionality in the AXU. A communications path386, however, is still provided between swizzle SPR's 374 and XU 368 toenable the XU to perform saves and restores of the swizzle SPR's duringcontext switching operations.

It will be appreciated that other manners of partitioning the swizzlelogic, storage elements and/or swizzle SPR's among the components of aprocessing unit may be used in other implementations consistent with theinvention. The invention is therefore not limited to the particularimplementations disclosed herein.

FIG. 12 next illustrates at 400 an exemplary sequence of operationsperformed by processing unit 300 of FIG. 9 in processing instructionsfrom an instruction stream. Upon receipt of an incoming instruction, adetermination is made in block 402 as to whether the instruction isvalid. If not, no further processing of the instruction is performed,and an error condition may optionally be signaled. If the instruction isvalid, however, control passes to block 404 to determine whether theinstruction is a persistent swizzle instruction. If not, indicating thatthe instruction is an arithmetic instruction for execution by vectorunit 304, control passes to block 406 to perform operand word reorderingaccording to the contents of the swizzle special purpose register 314for the associated thread. Control then passes to block 408 to performthe arithmetic operation requested by the instruction, and with theoperand vectors reordered as specified in the swizzle SPR for thethread. Processing of the instruction is then complete. Returning toblock 404, if the instruction is a persistent swizzle instruction,control passes to block 410 to update the swizzle SPR 314 for thecurrent thread, using the state information stored in the instruction.Processing of the instruction is then complete.

It may be desirable in some embodiments to specify a duration within apersistent swizzle instruction, such that the custom word orderingspecified by the instruction expires after a predetermined duration,e.g., after a predetermined number of subsequent arithmeticinstructions. Thus, for example, a persistent swizzle instruction couldspecify that the custom word ordering in the instruction be persistedfor the next 3 instructions, whereby the subsequent three instructionsin the instruction stream would be processed using the specified customword ordering. Then, once the duration had been reached, the wordordering for the thread would be restored to the default ordering.

FIG. 13 illustrates at 420 another exemplary sequence of operationsperformed by processing unit 300 in processing instructions from aninstruction stream, including support for duration-limited persistentswizzle instruction. In this embodiment, upon receipt of an incominginstruction, a determination is made in block 422 as to whether theinstruction is valid. If not, no further processing of the instructionis performed, and an error condition may optionally be signaled. If theinstruction is valid, however, control passes to block 424 to determinewhether the instruction is a persistent swizzle instruction. If not,indicating that the instruction is an arithmetic instruction forexecution by vector unit 304, control passes to block 426 to performoperand word reordering according to the contents of the swizzle specialpurpose register 314 for the associated thread. Control then passes toblock 428 to perform the arithmetic operation requested by theinstruction.

Returning to block 424, if the instruction is a persistent swizzleinstruction, control passes to block 430 to update the swizzle SPR 314for the current thread, using the state information stored in theinstruction. Block 432 then determines whether a duration has beenspecified in the persistent swizzle instruction. If not, processing ofthe instruction is complete. On the other hand, if a duration isspecified, block 432 passes control to block 434 to update a durationcounter for the thread based upon that specified in the persistentswizzle instruction. The duration counter may be maintained, forexample, in an SPR or in other storage elements coupled to the swizzlelogic. Once the duration counter is set, processing of the instructionis complete.

Returning to block 428, once the arithmetic operation specified by anon-swizzle instruction is performed in block 428, blocks 436-442 updatethe duration counter and determine whether to continue to persist thestate information maintained for the current thread in the swizzle SPR.Specifically, block 436 determines whether the duration counter for thethread is greater than zero. If not, no duration has been specified, soprocessing of the instruction is complete. Otherwise, if the durationcounter is greater than zero, block 436 passes control to block 438 todecrement the counter. Block 440 then determines if the decrementedcounter is equal to zero. If not, the current state information for thethread should be maintained for at least one more instruction, soprocessing of the instruction is complete. Otherwise, if the durationcounter is now zero, block 440 passes control to block 442 to reset theswizzle SPR for the current thread to the default state, and processingof the instruction is complete.

Returning now to the cross product example above, where four permuteoperations are conventionally required, with two of the four permuteoperations sharing a first custom word ordering, and the other two ofthe four permute operations sharing a second custom word ordering, itwill be appreciated that the two unique custom word orderings requiredfor the cross product may be implemented using two persistent swizzleinstructions, with those arithmetic instructions using the custom wordorderings following the respective swizzle instructions in theinstruction stream. In contrast to the use of permute instructions,additional vector registers are not required to store the shuffledoperand vectors back into the register file, nor are read-writedependencies introduced to stall the arithmetic operations until theshuffled operand vectors have been written back into the register file.In addition, in contrast to convention, non-persistent swizzleinstructions, half the number of swizzle instructions are required, thusreducing the number of instructions in the instruction stream.

It will be appreciated that various additional modifications may be madewithout departing from the spirit and scope of the invention. Forexample, alternative logic circuits to the specific arrangements ofmultiplexers shown herein may be used to selectively shuffle words froman operand vector. Furthermore, selective shuffling of operand words mayoccur at various stages in an execution pipeline, and may be combinedwith other execution logic so that other operations are performed withinthe same stage of the pipeline.

Other modifications will be apparent to one of ordinary skill in the arthaving the benefit of the instant disclosure. Therefore, the inventionlies in the claims hereinafter appended.

1. A circuit arrangement, comprising: processing logic configured toprocess instructions from an instruction stream, wherein theinstructions in the instruction stream are selected from an instructionset that defines a vector instruction and a persistent swizzleinstruction, and wherein the processing logic includes: a register fileincluding a plurality of vector registers configured to store operandvectors, wherein each operand vector includes a plurality of words;vector execution logic configured to retrieve operand vectors from theregister file and process the retrieved operand vectors responsive tovector instructions received by the processing logic; and at least onesoftware-accessible swizzle special purpose register architected intothe processing logic and configured to store state information for usein selectively shuffling words from operand vectors retrieved by thevector execution logic in connection with processing vector instructionsreceived by the processing logic; and swizzle logic coupled to theprocessing logic and configured to selectively shuffle words fromoperand vectors retrieved from the register file by the vector executionlogic in connection with processing of the retrieved operand vectors bythe vector execution logic, wherein the swizzle logic is configured to,in response to a first persistent swizzle instruction received by theprocessing logic, persist state information for the swizzle logic in theat least one swizzle special purpose register, and wherein the swizzlelogic is configured to, in response to a plurality of vectorinstructions received by the processing logic subsequent to reception ofthe first persistent swizzle instruction by the processing logic,selectively shuffle words from operand vectors retrieved from theregister file by the vector execution logic in connection withprocessing the plurality of vector instructions using the stateinformation persisted in the at least one swizzle special purposeregister.
 2. The circuit arrangement of claim 1, wherein the processinglogic is configured to execute instruction streams from a plurality ofthreads, wherein the at least one swizzle special purpose registercomprises a plurality of swizzle special purpose registers, wherein eachspecial purpose register is associated with one of the plurality ofthreads, wherein the swizzle logic is configured to, in response to apersistent swizzle instruction associated with a first thread among theplurality of threads, persist thread-specific state information in afirst swizzle special purpose register among the plurality of swizzlespecial purpose registers that is associated with the first thread, andwherein the swizzle logic is configured to, in response to a firstvector instruction associated with the first thread, selectively shufflewords from a first operand vector retrieved from the register file bythe vector execution logic using the state information persisted in thefirst swizzle special purpose register.
 3. The circuit arrangement ofclaim 1, wherein each operand vector includes N words, wherein theswizzle logic comprises N multiplexers, wherein each multiplexerincludes N inputs, an output, and a select input, wherein the swizzlelogic is configured to selectively shuffle words by selectivelyasserting the select inputs of the N multiplexers.
 4. The circuitarrangement of claim 3, wherein the N multiplexers are disposedintermediate of first and second stages in an execution pipeline,wherein the first and second stages respectively include first andsecond stage latches, wherein each stage latch includes N words, whereinthe N inputs of each multiplexer are coupled respectively to receive theN words from the first stage latch, and wherein the N words from thesecond stage latch are respectively coupled to receive the outputs ofthe N multiplexers.
 5. The circuit arrangement of claim 1, wherein thevector execution logic comprises a pipelined vector floating pointexecution unit.
 6. The circuit arrangement of claim 1, wherein thepersistent swizzle instruction includes an opcode field and a pluralityof operand vector fields, each operand vector field including aplurality of control bits that selectively shuffle each of the pluralityof words in each operand vector.
 7. The circuit arrangement of claim 6,wherein each operand vector includes N words, wherein the plurality ofcontrol bits in each operand vector field includes N word-specificfields, each word-specific field including log₂N bits that specify towhich of N words each word should be shuffled.
 8. The circuitarrangement of claim 7, wherein the vector execution logic comprises afloating point unit configured to operate on up to three vectoroperands, wherein each operand vector includes four words, wherein thepersistent swizzle instruction includes three operand vector fields, andwherein each operand vector field includes four word-specific fields,each of which including two bits.
 9. The circuit arrangement of claim 1,wherein the swizzle logic is further configured to persist the swizzlespecial purpose register in response to a flush of the vector executionlogic.
 10. The circuit arrangement of claim 1, wherein the at least oneswizzle special purpose register is configured to be initialized to adefault word order wherein the plurality of words from each operandvector are unshuffled.
 11. The circuit arrangement of claim 1, whereinthe first persistent swizzle instruction specifies a duration, andwherein the swizzle logic is configured to reset the at least oneswizzle special purpose register after expiration of the specifiedduration.
 12. The circuit arrangement of claim 11, wherein the durationincludes a selected number of instructions, and wherein the swizzlelogic is configured to reset the at least one swizzle special purposeregister in response to execution of the specified number ofinstructions subsequent to the first persistent swizzle instruction. 13.The circuit arrangement of claim 1, wherein the swizzle logic isconfigured to persist the state information in the swizzle specialpurpose register such that each vector instruction executed subsequentto the first persistent swizzle instruction will use the persisted stateinformation until a second vector instruction is received or a flushoccurs.
 14. An integrated circuit device including the circuitarrangement of claim
 1. 15. A program product comprising a computerreadable medium and logic definition program code resident on thecomputer readable medium and defining the circuit arrangement ofclaim
 1. 16. A method of operating a processing unit of the typeincluding vector execution logic configured to retrieve multi-wordoperand vectors from a register file and process the retrieved operandvectors responsive to vector instructions from an instruction stream,the method comprising: in response to a first plurality of vectorinstructions received by the processing unit, selectively shufflingwords from operand vectors retrieved from the register file by thevector execution logic in connection with processing the first pluralityof vector instructions using first state information persisted in atleast one software-accessible swizzle special purpose register; inresponse to a persistent swizzle instruction received by the processingunit subsequent to receiving the first plurality of vector instructions,persisting second state information in the at least one swizzle specialpurpose register; and in response to a second plurality of vectorinstructions received by the processing unit subsequent to receiving thepersistent swizzle instruction, selectively shuffling words from operandvectors retrieved from the register file by the vector execution logicin connection with processing the second plurality of vectorinstructions using the second state information persisted in the atleast one swizzle special purpose register.
 17. The method of claim 16,wherein the processing unit is configured to execute instruction streamsfrom a plurality of threads, wherein the at least one swizzle specialpurpose register comprises a plurality of swizzle special purposeregisters, wherein each swizzle special purpose register is associatedwith one of the plurality of threads, the method further comprising: inresponse to a persistent swizzle instruction associated with a firstthread among the plurality of threads, persisting thread-specific stateinformation in a first swizzle special purpose register among theplurality of swizzle special purpose registers that is associated withthe first thread; and in response to a first vector instructionassociated with the first thread, selectively shuffling words from afirst operand vector retrieved from the register file by the vectorexecution logic using the state information persisted in the firstswizzle special purpose register.
 18. The method of claim 16, whereinthe persistent swizzle instruction includes an opcode field and aplurality of operand vector fields, each operand vector field includinga plurality of control bits that selectively shuffle each of theplurality of words in each operand vector.
 19. The method of claim 18,wherein each operand vector includes N words, wherein the plurality ofcontrol bits in each operand vector field includes N word-specificfields, each word-specific field including log₂N bits that specify towhich of N words each word should be shuffled.
 20. The method of claim19, wherein the vector execution logic comprises a floating point unitconfigured to operate on up to three vector operands, wherein eachoperand vector includes four words, wherein the persistent swizzleinstruction includes three operand vector fields, and wherein eachoperand vector field includes four word-specific fields, each of whichincluding two bits.
 21. The method of claim 16, further comprisingpersisting the swizzle special purpose register in response to a flushof the vector execution logic.
 22. The method of claim 16, wherein thefirst persistent swizzle instruction specifies a duration, the methodfurther comprising resetting the at least one swizzle special purposeregister after expiration of the specified duration.
 23. The method ofclaim 22, wherein the duration includes a selected number ofinstructions, and wherein resetting the at least one swizzle specialpurpose register includes resetting the at least one swizzle specialpurpose register in response to execution of the specified number ofinstructions subsequent to the first persistent swizzle instruction. 24.The method of claim 16, further comprising persisting the stateinformation in the swizzle special purpose register such that eachvector instruction executed subsequent to the first persistent swizzleinstruction will use the persisted state information until a secondvector instruction is received or a flush occurs.